中村 将志

Palladium atoms deposited by vapor deposition on a template of n-alkane molecules on a Au(111) surface exhibit strongly anisotropic growth. In the initial stage, a Pd nanorod is grown with its length regulated by the chain length of the template molecule. Nanorod formation and subsequent anisotropic cluster growth are induced by interactions between the Pd atoms and unsaturated bonds created by the dehydrogenation of the n-alkane. Dehydrogenation is catalyzed by the deposited Pd atoms, which produce Pd trap sites. Dehydrogenation is confirmed by the change in the X-ray absorption fine structure spectra at the near carbon K-edge (C K-NEXAFS). The electronic states of the Pd clusters are considerably confined, which show d-band narrowing as observed in the Pd L3-NEXAFS spectra.

The effects of alkali meal cation on the surface oxidation and alcohol oxidation reactions on Au(111) have been investigated using surface X-ray diffraction and infrared spectroscopy. It is known that alkali metal cations strongly affect the alcohol oxidation reactions on Pt(111); however, the oxidation reactions on Au(111) do not depend on alkali metal cations. Infrared spectroscopy reveals the formation of adsorbed OH in LiOH and CsOH solutions below the second anodic peak at 1.3 V. This result indicates that surface oxidation processes do not depend on alkali metal cations below 1.3 V. The interfacial structure, including the outer layer, of an Au(111) electrode has been determined using X-ray diffraction in LiOH and CsOH. During the surface oxidation, the Au(111) surface in CsOH gets roughened more remarkably than that in LiOH above 1.3 V. Li+ has a protective effect against surface roughening. Thus, the cationic effect is weaker in the potential region lower than the second anodic peak, which does not affect the lifting of the surface reconstruction and the alcohol oxidation reactions.

The adsorption of hydroxide (OHad) on Pt has been studied on the low index planes of Pt using infrared reflection absorption spectroscopy (IRAS) in electrochemical environments. We discuss the correlation between the integrated band intensity of the bending mode of OH of Pt-OH (delta(PtOH)) and the charge density of the oxide formation of Pt. The band of dPtOH is observed around 1100 cm(-1), and the onset potential depends on the surface structure. The onset potential of dPtOH on Pt(110) and Pt(100) overlaps with the hydrogen adsorption/desorption potential region. The order of the integrated band intensity of delta(PtOH) at 0.9 V vs RHE is opposite to the order of the oxygen reduction reaction (ORR) activity. This finding supports that the OHad is one of the species deactivating the ORR.

A graphene nanoribbon is formed by the dehydrogenation reaction of n-alkane adsorbed on a Au(111) surface. The X-ray absorption spectra at the near carbon K-edge show the appearance of the out-of-plane 1s --> pi* resonance upon heating the n-C44H90 monolayer with the simultaneous disappearance of the 1s --> sigma*(CH)/R (R: Rydberg state) resonance. The pi* resonance located at 284.6 eV reflects a high edge density and is consistent with the ribbon shape, which was observed by scanning tunneling microscopy, and the C 1s XPS peak at 284.0 eV. (C) 2014 Elsevier B.V. All rights reserved.

The growth of gold on top of a n-alkane monolayer, which consists of lamellar assemblies with close-packed flat-lying chains, is observed by using scanning tunneling microscopy. The n-alkane monolayer sustains gold atoms, and penetration of the atoms into the monolayer is inhibited. The molecular conformation is unaffected and the arrangement is only slightly changed upon deposition of the gold atoms. Two-dimensional clusters are grown and a smooth monolayer is finally obtained.

Correlation between Pt oxide and the activity for the oxygen reduction reaction (ORR) has been investigated on the low index planes of Pt (Pt(111), Pt(100), and Pt(110)) using voltammogram and rotating disk electrode (RDE). Pt oxide is formed by holding the potential at 1.0 V vs. RHE. The ORR activity decreases with the increase of the time of Pt oxide formation. The order of the ORR activity is Pt(100) < Pt(111) < Pt(110) in 0.1 M HClO4 after the formation of Pt oxide. This order is identical with that without Pt oxides. Formation of hardly reducible Pt oxide deactivates the ORR activity on Pt(111) remarkably. The amount of Pt oxides (PtOH, PtO and hardly reducible Pt oxide) increases as Pt(100) < Pt(111) < Pt(110) at 1.0 V.

Transitional structures of Cs+ at the outer Helmholtz plane (OHP) have been determined using time-resolved X-ray diffraction during the double-layer charging/discharging on the Ag(100) electrode in CsBr solution. At the double-layer potential region at which c(2 X 2)-Br is formed on Ag(100), the transient current comprises two exponential terms with different time scales: a rapid and a slow one are due to the dielectric polarization of water molecules and the transfer of Cs+, respectively. The slow term is composed of different dynamic processes of Cs+ during charging and discharging. When the potential is stepped in the positive direction, the coverage of Cs+ at the OHP decreases. In this step, the transient X-ray intensity at the (0 0 1) reflection, which is sensitive to the OHP structure, shows that Cs+ is released from the OHP according to exponential function of time. The decay of transient intensity of X-ray has a time scale similar to that of the current transient measurement. On the other hand, the accumulation process of Cs+ from the diffuse double layer to the OHP comprises two different kinetic processes after a potential step in the negative direction: a rapid one is the accumulation of Cs+ near the outer layer, and a slow one is the structural stabilization of the Cs+ layer.

Real surface structures of Pd(110) = 2(111)-(111) and Pd(311) = 2(100)-(111) have been determined using surface X-ray scattering (SXS) at 0.5V (RHE) in 0.1M HClO4 saturated with Ar and O-2. Both surfaces have unreconstructed (1 x 1) structures. These results differ from those of Pt(110) and Pt(311) of which surfaces are reconstructed to (1 x 2) in 0.1 M HClO4. Interlayer spacing between the first and the second layer d(12) is expanded on Pd(110) in O-2 saturated solution, whereas the spacing d(12) on Pd(311) is larger than that of the bulk in both Ar and O-2 saturated solutions. (c) The Electrochemical Society of Japan, All rights reserved.

Catalytic activity of rare earth oxides (REOs) in the vapor-phase dehydration of 1,4-butanediol to produce 3-buten-1-ol varies with lattice parameters of REOs. In order to clarify the adsorption structure and the reaction mechanism, adsorption energy of 1,4-butanediol on bixbyite REO, such as SC2O3, Y2O3, Dy2O3, Ho2O3, and Er2O3, {222} surface was calculated with density functional theory (DFT), and paired interacting orbitals (PIO) calculation of the adsorption state between 1,4-butanediol and Er2O3 was executed. The DFT study elucidates that the catalytic activity is correlated with adsorption energy. The PIO study clarifies the interactions between the reactive atoms of 1,4-butanediol and Er2O3 surface: tridentate interactions between a position-2 hydrogen atom of diol and an oxygen anion on Er2O3 and between each OH group of diol and erbium cations on Er2O3, and an intramolecular repulsive interaction between the position-1 carbon atom and the oxygen atom of OH group are observed. These results suggest that the position-2 hydrogen atom is firstly abstracted by a basic oxygen anion and that the position-1 hydroxyl group is subsequently abstracted by an acidic erbium cation. Another OH group on position 4 plays an important role of anchoring the diol to the Er2O3 surface. Therefore, it is proved that the dehydration of 1,4-butanediol over REOs proceeds via acid-base concerted mechanism. (C) 2013 Elsevier B.V. All rights reserved.

Active sites for the oxygen reduction reaction (ORR) have been studied on n(111)-(111) and n(111)-(100) surfaces of Pt3Ni in 0.1 M HClO4 using rotating disk electrode (RDE). The activity for the ORR is decreased with the increase of the step atom density on n(111)-(111) surfaces. This fact is completely opposite to that of the same series of Pt on which the activity is enhanced at higher step atom density. The ORR gives the highest activity on n(111)-(100) surfaces of Pt3Ni with terrace atomic rows n = 3 and n = 5. These results show that the activity for the ORR of (100) step is superior to that of (111) step on Pt3Ni electrodes. (C) 2013 Elsevier B.V. All rights reserved.

The basal plane of graphene has been known to be less reactive than the edges, but some studies observed vacancies in the basal plane after reaction with oxygen gas. Observation of these vacancies has typically been limited to nanometer-scale resolution using microscopic techniques. This work demonstrates the introduction and observation of subnanometer vacancies in the basal plane of graphene by heat treatment in a flow of oxygen gas at low temperature such as 533 K or lower. High-resolution transmission electron microscopy was used to directly observe vacancy structures, which were compared with image simulations. These proposed structures contain C = O, pyran-like ether, and lactone-like groups.

Polarization-dependent X-ray absorption fine structure spectroscopy at the carbon near K-edge (C K-NEXAFS) is developed for a layer-by-layer analysis, by measuring the distribution of electrons emitted by X-ray absorption as a function of emission angles. The C K-NEXAFS spectra for multilayer n-C12H26 grown on a Pt(111) surface modified with monolayer graphene are separated on the basis of the depth of the layers. The spectral signal of n-C12H26 molecules in the first layer, which is in contact with the graphene substrate, is detected in the separated spectra corresponding to the lower layer in addition to the spectra of the monolayer graphene. The energy and polarization dependence of sigma(CH)*/R (R: Rydberg state) resonances indicate that the orientation of the carbon plane of flat-lying chains with respect to the graphene sheet in the first layer is perpendicular (edge-on) below the multilayer, and is parallel (flat-on) in the monolayer.

The oxygen reduction reaction (ORR) has been studied on the n(111)-(111) and n(111)-(100) series of Pt3Co using a hanging meniscus rotating disk electrode (HMRDE) in 0.1 M HClO4 (n is the number of terrace atomic rows). The activity for the ORR on the n(111)-(111) series, which is estimated by the specific activity at 0.90 V (RHE) j(k), increases linearly with an increase in the step atom density d(S). On the other hand, the activity for the ORR on the n(111)-(100) series increases linearly with an increase of d(S) on the surfaces with n >= 9. On the surfaces with n < 9, however, the activity for the ORR decreases with an increase of d(S). We find a correlation between the ORR activity and theta(OH) at the step on the assumption that all the oxide species are Pt-OH.

Active sites for the oxygen reduction reaction (ORR) have been studied on four series of the high index planes of Pt in O. 1 M HCIO 4 using rotating disk electrode. The ORR activity linearly increases with the increase of the step atom density on n(111)一(111)andn(ll1)一(100)seriesfrom n=∞to n = 5 where n is the number of terrace atomic rows. The ORR activities on the surfaces with (100) terrace are lower than those with (111) terrace. giving no orientation dependence. The ORR activity increases as n(100)一(111)くn(100)一(110)くn(111)ー(100)くn(l11)一(111). Pt (331) = 3 (111)一(111) has the highest activity for the ORR. Active sites for the ORR are assigned to(l11)terrace edge or terrace atomic row neighboring to the edge.Key Words: Oxygen reduction reaction，H igh index planes，S tep，T

X-ray photoelectron spectroscopy (XPS) is among the most powerful methods to determine the surface chemical properties of carbon materials. Because heat-treated graphite oxide includes various defects, analyses of the structure by XPS help us understand the structures of various carbon materials. Thus, XPS spectra of graphene-related materials containing various functional groups and other defects on edges and in the basal plane were simulated and full width at half maximums (FWHMs) and peak shifts were obtained by density functional theory calculation. Shifts of whole C1s spectra were influenced by the electron-withdrawing functional groups such as C=O-containing functional groups. FWHMs of the main peak of C1s spectra were influenced by mainly electron-withdrawing functional groups in addition to defects such as vacancy, pentagons, and heptagons. Analyses using only XPS provide us limited information, even though the peak tops and FHWMs of simulated XPS spectra are used for assignment. Combination use of peak shifts and FWHMs of XPS spectra, infrared spectroscopy, and density functional theory calculation provided more reliable assignments of defects including oxygen-containing functional groups of carbon materials than commonly used methods using only peak shifts of XPS spectra.

Structural effects on the oxygen reduction reaction (ORR) have been studied on the high index planes of Pt (n(1 1 1)-(1 II), n(1 1 1)-(1 00), n(1 0 0)-(1 1 1) and n(1 0 0)-(1 1 0)) using rotating disk electrode (RDE) in 0.1 M HClO4. The activity for the ORR increases with the increase of the step atom density on the surfaces with (1 1 1) terrace from n= infinity to n=5 (n is the number of terrace atomic rows), whereas the surfaces with (1 0 0) terrace do not show structural effects on the ORR activity. The activity of the surfaces with (1 1 1) terrace is higher than that on the surfaces with (1 0 0) terrace. The active sites for the ORR are located between the (1 1 1) terrace edge and the (1 1 1) terrace atomic row neighboring to the edge on Pt electrodes. (C) 2013 Elsevier Ltd. All rights reserved.

Surface and subsurface structures of PtSn surface alloy on Pt(111) were determined using in situ scanning tunneling microscopy (STM) and X-ray diffraction. Different ordered structures of the PtSn alloy layer were observed by STM in HClO4 at coverage of theta(Sn) <= 0.23. Superstructure of (root 3 X root 7)R19.1 degrees with small domain size was formed at theta(Sn) = 0.23. This structure promoted the catalytic activity for the ethanol oxidation reaction with high durability. X-ray structural analysis showed that the ratio of Sn in the subsurface was below 3(2)%, The PtSn alloy layer was mainly formed at the surface of the Pt(111) electrode. The Sn atoms protruded by 0.02 nm from the Pt layer, which was similar to the surface structure of Pt3Sn(111). One Pt atom in the (root 3 x root 7)R19.1 degrees structure contacts to one or two surrounding Sn atoms, which lead to the highest activity for the EOR.

The oxidation processes of a Pt(111) electrode in alkaline electrolytes depend on non-specifically adsorbed ions according to in situ X-ray diffraction and infrared spectroscopic measurements. In an aqueous solution of LiOH, an OHad adlayer is formed in the first oxidation step of the Pt(111) electrode as a result of the strong interaction between Li+ and OHad, whereas Pt oxidation proceeds without OHad formation in CsOH solution. Structural analysis by X-ray diffraction indicates that Li+ is strongly protective against surface roughening caused by subsurface oxidation. Although Cs+ is situated near the Pt surface, the weak protective effect of Cs+ results in irreversible surface roughening due to subsurface oxidation.

Lattice strain of Pt-based catalysts reflecting d-band status is the decisive factor of their catalytic activity toward oxygen reduction reaction (ORR). For the newly arisen monolayer Pt system, however, no general strategy to isolate the lattice strain has been achieved due to the short-range ordering structure of monolayer Pt shells on different facets of core nanoparticles. Herein, based on the extended X-ray absorption fine structure of monolayer Pt atoms on various single crystal facets, we propose an effective methodology for evaluating the lattice strain of monolayer Pt shells on core nanoparticles. The quantitative lattice strain establishes a direct correlation to monolayer Pt shell ORR activity.

Depth analysis using X-ray absorption fine-structure spectroscopy at the near carbon K-edge (C K-NEXAFS) was performed for self-assembled monolayers of 4-methylbenzenethiol (4-MBT) and 4-ethylbenzenethiol (4-EBT) on Au(1 11). On the basis of the polarization dependence of pi* resonance intensity, the benzene rings of 4-MBT and 4-EBT were found to be tilted by 30 +/- 10 degrees and 60 +/- 5 degrees with respect to the Au(1 1 1) surface, respectively. The spectra were separated into two components according to their depth by fitting the intensity decay curves of the electrons emitted by X-ray absorption. The spectra for lower segments exhibited bands at almost identical energies with different intensities depending on the polarization between 4-MBT and 4-EBT. In contrast, the spectra for upper segments including the alkyl groups showed a marked difference in the location of the sigma*(CC) resonance. The sigma*(CC) resonance of the ethyl group predominantly observed in the 15 incidence spectrum of 4-EBT indicated that the ethyl group was directed perpendicularly. (C) 2013 Elsevier B.V. All rights reserved.

The principles of grazing incidence X-ray diffraction (GIXD) are discussed. A sample of a crystalline material is composed of a surface region including its top layer and a bulk part. The effect of the surface region on the intensity of surface X-ray diffraction cannot be generally disregarded. With the grazing configuration this small intensity is optimized and the structural parameters of surfaces, interfaces, and thin films can be determined through the comparison between the estimated, or experimental, and calculated structure factors. For the estimation, the experimental procedures to measure GIXD profiles around reciprocal lattice points with the necessary corrections are presented. A synchrotron X-ray source and diffractometers employed to perform GIXD experiments are briefly described. We conclude with two examples of systems investigated by means of GIXD: an electrochemical interface of Ag(1 0 0) and an epitaxial thin film of Bi4Ti3O12 grown on a TiO2 (1 0 1) single crystal. © Springer-Verlag Berlin Heidelberg 2013.

The temperature-induced phase transition of the n-C36H 74 monolayer on the monolayer graphene grown on a Pt(111) surface is studied by X-ray absorption fine structure spectroscopy in the carbon near the K-edge (C K-NEXAFS). The C K-NEXAFS spectra of the n-C36H 74 monolayer is separated from the spectra of the monolayer graphene by subtraction. The σCC resonance predominantly observed in the normal incidence (NI) spectra is consistent with a chain axis lying flat on the graphene sheet at 120 K (crystalline phase) and 300 K (smectic phase). The σCH/R resonance at 287.2 eV is characteristic of the monolayer, which is attributed to the σCH orbitals distributed in an open space above the monolayer. The intensity ratio of the resonance for grazing incidence (GI) spectra with respect to that for normal incidence (NI) spectra decreases as a function of the temperature, which reflects the orientation change of the carbon plane with respect to the graphene sheet, from perpendicular (edge-on) to parallel (flat-on) orientation upon the crystalline-smectic transition, and the expansion of the intermolecular spacings upon further transition to the fluid phase at 400 K. © 2013 American Chemical Society.

Spectral separation methods for X-ray absorption fine structure spectroscopy at the near carbon K-edge are examined for an n-C 36H74 monolayer adsorbed on a monolayer graphene grown on a Pt(1 1 1) surface. The spectra of n-C36H74 and the monolayer graphene are separated by fitting decay curves obtained for all photon energies by detecting photoelectrons as a function of the ejection angle. The results are discussed in comparison with separation results obtained by subtracting the independently measured graphene spectra as a background. © 2013 Elsevier B.V.

The oxygen reduction reaction (ORR) have been studied on n(1 1 1)-(1 0 0) series of Pt using hanging meniscus rotating disk electrode (HMRDE) in 0.1 M HClO4 (n is the number of terrace atomic rows). The activity for the ORR, which is estimated by the reduction current density at 0.90 V (RHE)j(ORR,0.90V), increases linearly with the increase of the step atom density d(S) on the surfaces with 5 <= n. On the surfaces with n < 5, however, the activity for the ORR decreases with the increase of d(S). The deactivation of the ORR on the surfaces with n < 5 correlates with the formation of PtO-like species at the step. (C) 2012 Elsevier Ltd. All rights reserved.

Interfacial structures of cobalt(II) porphine (CoP) and 12,3,7,8,12,13,17,18-octaethyl-21H,23-H-porphine]cobalt(II) (CoOEP) have been studied on Au(111) electrode using electrochemical scanning tunneling microscopy (EC-STM), in-situ X-ray diffraction, and density functional theory (DFT) calculations. The adsorption of porphyrins affects the reconstruction of Au(111) surface. The adsorption of CoP causes a lifting of the reconstruction to a complete 1 x 1 structure of Au(111). On CoOEP modified Au(111), the unit cell periodicity of the reconstructed substrate structure expands compared with the root 3 x 23 structure of bare Au(111). The same expanded substrate structure was observed on Au(111) modified with OEP without the coordinated Co ion; the coordinated metal ion of the adsorbed porphyrin molecule does not affect the substrate structure. This result indicates that the interaction of conjugated pi electrons of porphyrin with the substrate is stronger than that of the coordinated Co ion. In-situ X-ray diffraction and DFT calculation support non-covalent interaction of porphyrins with the Au(111) surface. (C) 2012 Elsevier B.V. All rights reserved.

The dissolution of cubic and tetrahedral Pt nanoparticles has been studied on a Pt plate in 0.1 M NaCIO4 using conventional in situ atomic force microscopy (AFM). The Pt nanoparticles were dissolved during the potential cycle between 0.0 and 1.1 V (Ag/AgCl). The sides of the nanoparticles are dissolved faster than the upper parts. The height of cubic Pt nanoparticles does not change up to 200 cycles, shrinking to 80% of the initial height after 600 cycles. Tetrahedral Pt nanoparticles are dissolved from the top, forming a terrace at the upper part after 300 cycles. The durability of cubic Pt nanoparticles is higher than that of tetrahedral Pt nanoparticles.

1D hydrogen bond chains of D2O molecules formed on a Pt(211) stepped surface are observed by polarization dependent near O K-edge X-ray absorption fine structure spectroscopy (O K-NEXAFS). The 1s -> sigma*(OD) resonance at 535.0 eV in the normal incidence O K-NEXAFS spectrum corresponds to the free OD bond oriented perpendicularly to the step lines, and the resonance at 540.0 eV is related to the hydrogen bond extended in a zigzag manner parallel to the step lines. A structural model consistent with these observations is obtained from the DFT optimization, in which all of the molecules act as one hydrogen donor and acceptor in the 1D chain.

Dissolution mechanism of cubic Pt nanoparticles has been studied with the use of atomic force microscopy on a carbon substrate in 0.1 M NaClO4. The shape of the nanoparticles does not change in the double layer region. The height of the nanoparticles increases slightly at the onset potential of the oxide film formation. The nanoparticles are dissolved from the sides in the oxide film formation region, whereas the change of the height is negligible. These results differ from those of the cubic Pt nanoparticles on a Pt substrate, on which the dissolution proceeds at the upper terrace. (C) 2011 Elsevier B.V. All rights reserved.

We revealed the promotive effect of alkali metal cations on Br adlayer formation on an Ag(100) electrode by in-situ measurement of the x-ray specular rod. Alkali metal cations in the electrical double layer affect the onset potential of Br adsorption and the order-disorder transition. We determined the Cs structure in the electrical double layer during Br adlayer formation and found that (1) the Cs structure depends on the coverage of adsorbed Br, and (2) the amount of Cs increases at the initial stage of Br adlayer formation. Structural analysis suggests that hydrated Cs is localized in the area around adsorbed Br via noncovalent interactions. Formation of a Cs-Br complex promotes Br adsorption. © 2011 American Physical Society.

Adsorbed hydrogen and water were measured during the hydrogen evolution reaction (HER) on the low and high index planes of Pt in 0.5 M H2SO4 using infrared reflection absorption spectroscopy. Hydrogen is adsorbed at the atop site (atop H) on Pt(110) during the HER, whereas adsorbed hydrogen at the asymmetric bridge site (bridge H) is found on Pt(100). The band intensity of the adsorbed hydrogen depends on temperature, indicating that the bands are due to the intermediate species for the HER. The band of the atop H appears on stepped surfaces with (110) step, whereas the asymmetric bridge H is observed on Pt(211) = 3(111)-(100) and Pt(311)= 2(111)(100) that have (100) step. The absence of the atop H on Pt( 100). Pt(211), and Pt(311) can be attributed to the relative stability of the bridge site. (C) 2011 Elsevier B.V. All rights reserved.

The oxygen reduction reaction (ORR) have been studied on n(1 1 1)-(1 0 0) series of Pd using hanging meniscus rotating disk electrode (HMRDE) in 0.1 m HClO(4) saturated with O(2). Activity for the ORR, which is estimated by the reduction current density at 0.90 V (RHE) j(ORR,0.90V). is enhanced linearly with the increase of the terrace atom density d(T), showing that (1 1 1) terrace is the active site for the ORR on n(1 1 1)-(1 0 0) series of Pd. Coverage of the oxide film theta(OX) of Pd increases with the increase of d(T) at 0.90 V (RHE). The correlation of the ORR activity and theta(OX) contradicts to that on Pt electrodes on which the ORR is deactivated with the increase of theta(OX) The oxide film is not relevant to the ORR on n(1 1 1)-(1 0 0) series of Pd at 0.90 V (RHE). (C) 2011 Elsevier B.V. All rights reserved.

Structural effects on the hydrogen oxidation reactions (HOR) and the hydrogen evolution reactions (HER) have been studied on (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1), n(1 0 0)-(1 1 0) and n(1 1 1)-(1 0 0) series of Pt using rotating disk electrode (RDE) in 0.1 M HClO(4) saturated with H(2). The value of the exchange current density J(0) increases linearly with the increase of the step atom density d(S) from n = infinity to n = 9, where n denotes the number of terrace atomic rows, on (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1), and n(1 0 0)-(1 1 0) series. This indicates that the activity for the HOR/HER of the step is higher than that of the terrace. The values of j(0) of (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1) and n(1 0 0)-(1 1 0) series become constant on the surfaces with n <= 9, whereas those of n(1 1 1)-(1 0 0) series increase with the increase of d(S). The activity for the HOR/HER per step atom increases in the sequence: n(1 1 1)-(1 0 0) < n(1 0 0)-(1 1 1) < n(1 0 0)-(1 1 0) < (n-1)(1 1 1)-(1 1 0). This result supports that the most active site for the HOR/HER is the linear (1 1 0) step. Decrease of the NOR current is found around 0.2 V(RHE) on the surfaces with (1 0 0) terrace, whereas the surfaces with (1 1 1) terrace give no decrease of the HOR current. (C) 2011 Elsevier B.V. All rights reserved.

One to three layers of Ag grown on a Au(111) electrode were studied by cyclic voltammetry in chloride and bromide solutions and by ex-situ near-edge X-ray absorption fine structure spectroscopy at the Ag L3-edge (Ag L3-NEXAFS). The one and two layers obtained by underpotential deposition exhibited reduced intensity at the absorption edge in the Ag L3-NEXAFS spectra, which suggests the gain of d-electrons in these layers. The cyclic voltammograms and the Ag L3-NEXAFS spectra indicate that the second and third layers of Ag halogenated at positive potentials, whereas the first layer remained in metallic form. (C) 2011 Elsevier B.V. All rights reserved.

Surface structures of Pd(111) and Pd(100) electrodes have been determined at 0.50 V (RHE) in 0.1 M HClO4 saturated with Ar or O-2 using surface X-ray scattering (SXS). Both surfaces have unreconstructed (1 x 1) in-plane structure. The surface layers on Pd(111) do not relax in Ar saturated solution: the interlayer spacing between the first and the second layers d(12) agrees with that of the bulk. In O-2 saturated solution, the value of d(12) is expanded by 1.8% on Pd(111), whereas the value of d(23) (interlayer spacing between the second and third layers) is the same as that of the bulk. No relaxation is also observed on Pd(100) in Ar saturated solution. In O-2 saturated solution, however, d(23) as well as d(12) is expanded by 5.7% on Pd(100).

Near edge X-ray absorption fine structure spectra at the carbon K-edge (C K-NEXAFS) of n-C(12)H(26) films grown on graphite (0 0 01) were measured under ultrahigh vacuum conditions. In the normal incidence spectra, the 1s -> sigma*(CH)/R resonance of n-alkane was identified at a lower energy than the absorption edge of graphite. The sigma*(CH)/R resonance directed along the CH bond was observed at 286.9 eV for the first layer of the n-C(12)H(26) film on graphite. This indicates that the CCC plane of the molecule is parallel to the surface (fiat-on orientation). As the film thickness increases, another peak assigned to sigma*(CH)/R(perpendicular to) grows at 288.0 eV, suggesting an increase in the number of molecules with the CCC plane perpendicular to the surface in a multilayer film. (C) 2011 Elsevier B.V. All rights reserved.

Real surface structures of the high-index planes of Pt with three atomic rows of terraces (Pt(331) = 3(111)-(111) and Pt(511) = 3(100)-(111)) have been determined in 0.1 M HClO4 at 0.1 and 0.5 V(RHE) with the use of surface X-ray scattering (SXS). The surfaces with two atomic rows of terraces, Pt(110)= 2(111)4111) and Pt(311) = 2(100)-(111) = 2(111)(100), are reconstructed to a (1 x 2) structure according to previous studies. However, the surfaces with three atomic rows of terraces have pseudo-(1 x 1) structures. The interlayer spacing between the first and the second layers, d(12), is expanded 13% on Pt(331) compared to that of the bulk, whereas it is contracted 37% on Pt(511). The surface structures do not depend on the applied potential on either surface.

An incommensurate crystalline phase of the (sub)monolayer of n-C(36)H(74) lying on graphite (0001) is observed on cooling the smectic phase using normal incidence near edge X-ray absorption fine structure spectroscopy at the carbon K-edge (NI C K-NEXAFS) and scanning tunneling microscopy (STM). The orientation of the CCC plane of the all-trans alkyl chain with respect to the substrate is confirmed by the 1s -> sigma(CH)*/R resonance detected by the NI C K-NEXAFS spectra at the absorption edge. Almost all molecules take the parallel (flat-on) orientation in the smectic phase, and at least half of them change to the perpendicular (edge-on) orientation in the incommensurate crystalline phase. A lamellar structure with a width corresponding to the chain length and no internal structure is observed by STM in the smectic phase, whereas that in the incommensurate crystalline phase exhibits a ladder-like structure with a periodicity of ca. 2 nm transverse to the chain direction. The periodicity is incommensurate with the substrate lattice. The molecular orientation in the ladder-like structure is related to the molecular width varying from 0.43 to 0.63 nm in the magnified STM image.

The surface structure of underpotentially deposited Bi has been determined on Au(111) in perchloric acid solution using surface X-ray diffraction (SXD), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. SXD analysis and STM images reveal that the catalytically active structure for the hydrogen peroxide reduction reaction (HPRR) is the (2 x 2)-Bi honeycomb Structure with theta(Bi) = 0.50. The stability is supported by DFT calculations. The hydrated perchlorate anion is located in the center of the honeycomb structure without hydrogen peroxide. DFT calculations predict that the Bi honeycomb structure promotes the dissociation of the O-O bond of hydrogen peroxide. Hydrogen peroxide expels the hydrated perchlorate anion, and then HPRR takes place at the honeycomb center.

Real structure of cubic Pt nanoparticle has been studied at various potentials in 0.1 M NaClO4 with the use of atomic force microscopy (AFM). Cubic Pt nanoparticles in 10 nm height are clearly imaged from 0.10 V to 1.10 V (Ag/AgCl). The height of the nanoparticle increases 1.2 +/- 0.7 nm (10.4 +/- 6.8%) around the onset potential of oxygen evolution (1.20 V (Ag/AgCl)). The height increase is attributed to the formation of the oxide species at the inner layers of the nanoparticle. Dissolution of the nanoparticle starts from the upper terrace, not from the edge above 1.40 V (AgiAgCl). (C) 2010 Elsevier B.V. All rights reserved.

Oxygen reduction reaction (ORR) has been studied on the low index planes of Pd modified with a monolayer of Pt (Pt/Pd(hkl)) in 0.1 M HClO(4) with the use of hanging meniscus rotating disk electrode. The activity for ORR on bare Pd(hkl) electrode depends on the surface structure strongly, however, voltammograms of ORR on Pt/Pd(hkl) electrodes do not depend on the crystal orientation. The specific activities of Pt/Pd(hkl) electrodes at 0.90 V (RHE) are higher than that on Pt(110) which has the highest activity for ORR in the low index planes of Pt. The mass activity on Pt/Pd(hkl) electrode is 7 times as high as a commercial Pt/C catalyst. (C) 2009 Elsevier B.V. All rights reserved.

A rapid X-ray diffraction method was proposed for in situ observation of a surface-intermediate structure on a liquid-solid interface. It used a combination of higher-energy monochromatic synchrotron X-rays in grazing incidence and an X-ray two-dimensional detector. Overall patterns were in situ taken, with one-time exposure, of the reciprocal-lattice space of a Au (1 1 1) electrode surface which was fixed at an angular position. We deduced change in crystal domain shapes of surface intermediates as well as its smaller lattice distortion by observing images of reconstructed surface rods during a surface-structural phase transition from the reconstructed surface to the bulk terminated surface. An anisotropic shape of surface-crystal domains was also observed. (C) 2009 Elsevier B. V. All rights reserved.

Structural effects on hydrogen oxidation and evolution reactions (HOR/HER) have been studied on n(111)-(111) surfaces of Pt using a rotating disk electrode in 0.1 M HClO(4) saturated with H, at temperatures between 268 and 298 K. The exchange current density of HOR increases linearly with the increase of step atom density up to the surface with the terrace atomic rows n = 9; however, it becomes constant on the surfaces with n <= 9. The activation energy and pre-exponential factor of HOR/HER decrease with the increase of the step atom density, but they also become constant on the surfaces with n <= 9. These results support that the step atom is the active site of HOR/HER; however. a part of the step atoms contributes to HOR/HER on the surfaces with n <= 9.

Surface structures of shape-controlled Pt nanoparticles have been estimated using cyclic voltammetry (CV) and infrared reflection absorption spectroscopy (IRAS). Cubic and cubocatahedral Pt nanoparticles are prepared using a capping polymer. These nanoparticles give CVs similar to those of single crystal electrodes of Pt in sulfuric acid solution. The CV of cubic nanoparticles is similar to that of the Pt(510) [=5(100)-(110)] electrode, while the CV of cuboctahedral nanoparticles is reproduced well with the convolution of Pt(766) [=13(111)-(100)] and Pt(17 1 1) [=9(100)-(111)] electrodes. These results suggest that the planes of the cubic and cuboctahedral nanoparticles are composed of step-terrace and atomically flat terraces, respectively. Adsorbed carbonmonoxide (CO) on the shape-controlled nanoparticles gives the IR bands that are assigned to on-top and bridged CO. The band of on-top CO is deconvoluted to two bands: the higher and the lower frequency bands are assigned to the CO on the plane and the edges of the nanoparticles, respectively. on top CO adsorbed on the edges is oxidized at more negative potential then that on the planes. Edge sites of the nanoparticles promote CO oxidation.

Active sites for the oxygen reduction reaction (ORR) have been studied on the low index planes, n(100)(111) and n(100)-(110) series of Pd with the use of hanging meniscus rotating disk electrode (RDE) in 0.1 M HClO(4) saturated with O(2). The Kotekey-Levich plots give a linear line with a slope of about 4, showing four electron reduction for the ORR on Pd electrodes, as is the case of Pt. Activity of ORR, which is estimated by the reduction current density at 0.90 V (RHE) j(ORR.0.90V), gives the following order on the low index planes: Pd(110) - Pd(111) < Pd(100). This order is completely opposite to that of Pt in 0.1 M HClO(4): Pt(100) < Pt(111) < Pt(110). Specific activity of Pd(100) is nearly three times as high as that of Pt(110) at 0.90 V (RHE). The values of j(ORR,) (0.90) (V) increase linearly with the increase of the terrace atom density on n(100)-(111) and n(100)-(110) series of Pd. This fact supports that (100) structure is the active site for ORR on Pd. ORR activity does not depend on the step structure of n(100)-(111) and n(100)-(110) series.

We determined the structure of water at step edges on the stepped Pt(211) = 3(111)-(100) surface using surface X-ray diffraction. Adsorbed water molecules form a chain with a zigzag configuration along the step line through hydrogen bonds. The chain comprises two types of water molecules. One is adsorbed on the top of the step atom and has a shorter Pt-O distance than that adsorbed on terrace sites, which indicates stronger adsorption at step edges. The other is displaced from the precise on-top sites and has an elongated Pt-O distance. The hydrogen-bonding configuration of the water chain is different from the tetrahedral arrangement of ice. The interaction of the water molecules with the surface distorts the hydrogen bonds in the water chain.